Process for preparing acrylic acid and or methacrylic acid from acrolein or methacrolein

ABSTRACT

A process for preparing acrylic acid or methacrylic acid which comprises reacting acrolein or methacrolein with molecular oxygen in the presence of a catalyst consisting essentially of (a) molybdenum, (b) phosphorus, (c) at least one element selected from the group consisting of niobium, tantalum and titanium, and (d) oxygen, as the essential components, and (e) at least one element selected from the group consisting of tin, nickel, magnesium, tungsten, bismuth and iron, as an optional component.

United States Patent 1191 Oda et a1.

[ PROCESS FOR PREPARING ACRYLIC ACID AND OR METHACRYLIC ACID FROM ACROLEIN OR METHACROLEIN [75] Inventors: Yoshio Oda; Keiichi Uchida;

Takeshi Morimoto, all of Yokohama, Japan [73] Assignee: Asahi Glass Co., Inc., Tokyo, Japan [22] Filed: Oct. 20, 1972 [21] Appl. No.: 299,383

[30] Foreign Application Priority Data Oct. 22, 1971 Japan 46-83343 Dec. 16, 1971 Japan 1 1 46-101456 Mar. 7, 1972 Japan 47-22756 Mar. 7, 1972 Japan 47-22757 1521 [1.5. CI. 260/530 N, 252/437 [51] Int. Cl. C07c 57/04 [581 Field of Search 260/530 N, 533 N [56] References Cited UNITED STATES PATENTS 3,087,964 4/1963 Koch et a1. 260/530 N 3,230,248 1/1966 Yamagita et a1... 260/530 N 3,280,182 10/1966 Gasson et a1, 260/530 N 3,322,693 5/1967 Bethell et a1 260/530 N 1 1 Feb. 11, 1975 3,365,489 1/1968 Bethell et a1 260/530 N 3,435,069 3/1969 Bethell et a1 3,544,624 12/1970 Anderson et a1. 260/530 N 3,557,199 1/1971 Parthasarathy et a1 260/530 N 3,639,269 1/1972 Koberstein et a1 260/530 N 3,761,424 9/1973 Koherstein et a1 1. 260/530 N FOREIGN PATENTS OR APPLICATIONS 41-1407 2/1966 Japan 260/533 N 41-14900 8/1966 Japan 260/530 N Primary Examiner-Lorraine A. Weinberger Assistant Examiner--Richard D. Kelly Attorney, Agent, or Firm-Ob1on, Fisher, Spivak, McClelland & Maier [57] ABSTRACT 7 Claims, No Drawings PROCESS FOR PREPARING ACRYLIC ACID AND OR METHACRYLIC ACID FROM ACROLEIN OR METI-IACROLEIN BACKGROUND OF THE INVENTION I. Field of the Invention This invention relates to a process for preparing acrylic acid or methacrylic acid by the catalytic vapor phase oxidation of acrolein or methacrolein. More particularly, the invention relates to a process for preparing methacrylic acid from methacrolein, characterized mainly by the use of novel catalysts.

2. Description of Prior Art Conventionally, many catalysts useful for the preparation of unsaturated carboxylic acids having from three to four carbon atoms by the catalytic vapor phase oxidation of the corresponding unsaturated aldehydes with molecular oxygen have already been proposed. Some of those catalysts are excellent for preparing acrylic acid from acrolein and have been used for the large scale production of acrylic acid. Various catalysts for preparing methacrylic acid from methacrolein have also been proposed. However, by the use of those catalysts the methacrylic acid has not been produced from methacrolein commercially because of the low yield. This is because methacrolein is more combustible than acrolein, and being subjected to complete oxidation to carbon monoxide and/or carbon dioxide rather than to partial oxidation to the desired product. Thus up to the present, an excellent catalyst used for the preparation of methacrylic acid has not yet been found.

Catalyst in the US. Pat. Nos. 3,358,020 and 3,435,069, for example, showed the excellent performance for the production of acrylic acid (the conversion of acrolein is 96 100%, the selectivity of acrylic acid is 80 90% but not for the production of methacrylic acid (the conversion of methacrolein is 29 63%, the selectivity of methacrylic acid is ll 41%).

SUMMARY OF THE INVENTION It is an object of this invention to provide a method for not only preparing methacrylic acid in superior yield in comparison with prior arts, but also preparing acrylic acid in a superior yield.

Another object is to-provide a novel catalyst for the preparation of unsaturated carboxylic acids from corresponding unsaturated aldehydes and a method for the preparation thereof.

Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description and disclosure.

This invention provides a process for preparing acrylic acid or methacrylic acid by the oxidation of acrolein or methacrolein with molecular oxygen in vapor phase at a temperature of from 250 to 450C, in the presence of a catalyst consisting of (a) molybdenum, (b) phosphorus, (c) at least one element selected from the group consisting of niobium, tantalum and titanium, and (d) oxygen, as the essential components, and (e) at least one element selected from the group consisting of tin, nickel, magnesium, tungsten, bismuth and iron, as an optional component.

According to the process of the invention, in preparing methacrylic acid from methacrolein, for example, the conversion of methacrolein and the selectivity of methacrylic acid were 60 70% and 75 83%, re-

spectively and also in preparing acrylic acid from acrolein, the conversion of acrolein and the selectivity of acrolein acid were 95 100% and respectively.

Catalysts are capable of having the desired catalytic activity, only when the catalysts contain all the essential components. When catalysts lack any one or two components of essential ones, the activity of such catalysts is remarkably low, producing small amounts of the desired unsaturated carboxylic acids. Thus these catalysts are unsatisfactory for the commercial application.

So far as the catalysts of this invention contain all the essential components above, they have considerably good catalytic activity, preferably in case of assigning the number of molybdenum atoms as 12, the catalysts having the following empirical formula show superior catalytic activity:

wherein X is at least one element selected from the group consisting of Nb, Ta and Ti; 0: is a number of 0.1 to 5, preferably 0.2 to 3; B is a number of 0.1 to 10, preferably 0.3 to 5; 'y is decided on the basis of oxidized states of Mo, P and X, and when each component is in highly oxidized state, y is a number of 37 to 81.

In particular, the preferred catalysts of this invention may be expressed in the following three formulas:

MO12P a wherein a is a number of 0.3 to 3; B is a number of 0.5 to 3; y is a number of 37 to 56.

wherein a is a number of 0.5 to 2;, B is a number of 0.5 to 3; 'y is a number of 34 to SI.

wherein a is a number of 0.2 to 3; B is a number of 0.3 to 5; y is a number of 37 to 54.

In addition to the essential components above, the catalysts of this invention may contain at least one element selected from the group consisting of Sn, Ni, Mg, W, Bi and Fe, thereby improving their catalytic activity. These elements are not essential components but optional components.

When the catalysts of this invention contain the optional components above, their preferred empirical formula may be expressed as follows:

M0 P a Y 8 "-06 wherein X is at least one element selected from the group consisting of Nb, Ta and Ti;Y is at least one element selected from the group consisting of Sn, Ni, Mg, W, Bi and Fe; a is a number of 0.1 to 5, preferably 0.2

to 3', B is a number of 0.1 to 10, preferably 0.3 to 5; 6

is a number of 0.1 to 10, preferably 0.5 to 3; e is decided on the basis of oxidized states of Mo, P, X and Y, and when each component is in highly oxidized state, e is a number of 38 to 111.

The foregoing catalysts of this invention may contain any further elements unless they injure the catalytic activity.

The catalysts of this invention may be prepared by several methods. Preferably, the catalysts may be prepared by concentrating a solution or a suspension containing the requested components, followed by drying the resulting concentrate. Thereafter, preferably the dried product is calcined at a temperature of from 250 The contact time may be usually from 0.2 to 30 secto 450C, for about 1 to about 48 hours in art. Then, d f r bl from 1 to 20 seconds. the Cale natiolt Product S g into the SiZe f 5 The molar ratio of oxygen to unsaturated aldehydes mesh to 100 mesh suitable for use. Thus prepared catai h feed gas supplied to the reactor may usually be lyst have 0.1 to 50 m /g of a specific surface area. 5 from 1:10 to :1, preferably from 1:3 to 3:1.

In me cases, n r r to impro h phy i l pr p- Steam maybe added to the gaseous reactant mixture y of the catalysts ,tt is Preferred to pp the eateabove, thereby improving the yield of unsaturated carlysts on a suitable carrier, such as, silica, silicacontainb li ld F h nitrogen, saturated h d ing-materials, silicon carbide, alumina and the like. The b h methane, propane, butane or the like, or amount of the carrier used is preferably in the range of 10 other inert gas may be also added to said gaseous reac- 30 to 97% by weight based on the supported catalysts. tant mixture. The concentration of the steam may vary The exact chemical structure of the catalysts of this within the range from 2 to 80%, preferably from 10 to invention is not clear. However, it can be presumed, 50% by volume of the feed. that the catalyst may be a homogeneous mixture of ox- Since the reaction of this invention is exothermic, the

ides of all the components, or may be a compound or 1 temperature within the reactor must be regulated in a complex formed by means of the mutual reaction of order to control the reaction. Thus, it is preferred that salt of molybdenum and phosphorus, and the oxides of the reactor is placed in a fluidized solid bath, a molten the other components. salt bath or a metal bath.

The starting materials of each component used for The methacrylic acid or acrylic acid may be recovthe preparation of the catalysts of this invention are as cred from the reaction products by any conventional follows: As a molybdenum source, ortho-, metaor methods, for example, by condensation or extraction para-molybdic acid, ortho-, metaor paramolybdates with water followed by distillation. heteromolybdic acid, heteromolybdates, molybdenum Wherein the following definitions are applied to the oxide or the like, preferably ammonium paramolybdate conversion of unsaturated aldehydes, and the selectivmay be used. As a phosphorus source, phosphoric acid, ity and the yield of unsaturated carboxylic acids. All phosphates, polyphosphoric acid, polyphosphates may the analyses were conducted by means of gas chromabe used. Phosphomolybdates may effectively be used as tography.

Unsaturated aldehyde Unsaturated aldehyde Conversion in the feed (mole in the effluent molel x 100 (percent) Unsaturated aldehyde 1n the fee mo e Selectivity (percent) Unsaturated carboxylic acid in the effluent (mole) x 100 Unsaturated aldeh de Unsaturated a e y e in the feed (mole) in the effluent (mole) a common starting material for molybdenum and phos- Yield (percent) Conversion X Selectivity 1/100 Phorus Soufee- AS a niobium Source, niobium OXide, 40 The process of the invention is further illustrated by obium hydroxide, niobium oxalate or the like; as a tanh f ll i examples, talum component, tantalum pentoxide, tantalum oxa- A series f rim t was conducted with a U- late or the like; as a titanium source, titanium trichloh d stainless steel r act r 400 mm long and of 6 mm ride, titanium dichloride, titanium nitrate oxide, titainner di The r t was filled with 4 m1 of a Ilium diOXide Or the like; as a tin Source, tin Oxide tin catalyst which was made according to each of following chloride or the like; as a tungsten source, tungsten triexamples, Th reactor was put i a molten n oxide, tungstic acid, tungstates or the 1ike;aS a bismuth sium nitrate bath heated at the reaction temperature. Source, bismuth ni sm OXide Or the like; as an The reactant gaseous mixture was fed into said reactor iron source, iron nitrate, iron chloride or the like; as a d the efflnent from said reactor was led to a conmagneSium Source, mag nitrate, magnesium denser cooled with a dry-ice ethanol bath. The unconchloride or thC k6; as a nickel SOUTCC, nickel nitrate, densed gas was analyzed means of gas chromatogranic e Chloride O the k my effectively be Used, phy. While the condensate containing an unsaturated spectively. aldehyde and an unsaturated acid was also analyzed by The essential reactants of this invention are unsatumeans of g s chromatography, rated aldehyde, namely, acrolein or methacrolein and molecular oxygen which may be pure oxygen, oxygen EXAMPLE I diluted with inert gases oxygen enriched air or air with- 23,1 grams of thophos h rie acid dissolved in out additional yg In View of my. all is the 50 ml of water were added, under stirring, to a liquid most practical source of molecular oxygen. which dissolved 423 grams of ammonium paramolyb- The reaction of this invention may be carried out in 0 date, (NH Mo-,O .4H O, in 700 ml of water 26.6 either a fixed or fluidized catalyst bed. The reaction grams f i bi m t ide, Nb o susp ded in temperature may vary Within he ang frOm to ml of nitric acid aqueous solution (1:1) was added to 450C, preferably from 300 to 400C. The rea the mixture liquid above. Then, the resulting liquid was Pressure y y Within the range of from to 40 concentrated by means of heating under stirring, folatmospheres absolute, preferably from about 1 to 10 5 l d b d i f th resulting slurry at C f r 16 atmospheres absehltewhen the reaction Pressure is hours. Thereafter, the dried product was calcined at relatively higher within said range, the reaction tempe 400C for 12 hours, whereby a solid having the followature may be somewhat lower Within S g ing atomic ratio of the elements was obtained.

Said solid was sieved to collect a catalyst within the range of 35 to 100 mesh size. The aforementioned U- shaped reactor was filled with 4 ml of the obtained catalyst. The reactor was put into the molten salt bath heated at 340C. A reactant gaseous mixture composed of of methacrolein, 9% of oxygen, 32% of steam and 54% of nitrogen, the percentages being by volume, was passed through the reactor with a contact time of 2 seconds. The following results were obtained:

The conversion of methacrolein: 62.5%

The selectivity of methacrylic acid: 738% The selectivity of acetic acid: 8.2%

EXAMPLES 2-5 Catalysts were prepared in the similar way to that of Example 1, except that the starting materials were adjusted so as to maintain the atomic ratios given in Table l. The catalysts were used for the oxidation of methacroleln under substantially the same conditions as those employed in Example 1. The results obtained are given in Table 1:

Table l Methac ro- Methacrylic Acetic lein acid acid Ex. conversion selectivity selectivity Nos. Catalysts 11) 2 Mo, P,Nb O, 53.7 63.1 7.4 3 M0,,P,Nb,0., 32.2 72.2 6.1 4 Mo, P,Nb,O 43.8 49.5 8.3 5 Mo, P Nb,O:, 16.1 78.3 5.3

REFERENCE EXAMPLES l-5 Catalysts were prepared in the similar way to that of Example 1, except that the starting materials were adjusted so as to maintain the atomic ratios given in Table 2. As iron and nickel components, nitrates were used, respectively. The catalysts were used for the oxidation of methacrolein under substantially the same conditions as employed in Example 1. The results obtained were given in Table 2:

EXAMPLES 6l0 (atalysts were prepared in the similar way to that of Example 1, except that the starting materials were adjusted so as to maintain the atomic ratios given in Table 3. The catalysts were used for the oxidation of acrolein under the same conditions as employed in Example 1, except that the reaction temperature was 360C. The results obtained were given in Table 3.

23.1 grams of orthophosphoric acid dissolved in 50 ml of water were added, under stirring, to the liquid in which was dissolved 423 grams of ammonium paramolybdate in 700 ml of water. 97.0 grams of his muth nitrate, Bi(NO .5l-l O, dissolved in 300 ml of nitric acid (1:1) was added all at once to the mixture liquid above under stirring and further, 26.6 grams of niobium pentoxide suspended in ml of nitric acid (1:1) was added to the resulting liquid. Then, the resulting mixture liquid was concentrated by heating under stirring, followed by drying of the obtained slurry at C for 16 hours. Thereafter, the dried product was calcined at 400C for 12 hours, whereby a solid having the following atomic ratio of elements was obtained.

Said solid was sieved to collect a catalyst within the range of 35 to 100 mesh size. The aforementioned U- shaped reactor was filled with 4 ml of the obtained catalyst. The catalysts were used in the oxidation of meth acrolein under substantially the same conditions as those employed in Example 1. The following results were obtained:

The conversion of methacrolein: 82.5%

The selectivity of methacrylic acid: 75.6%

The selectivity of acetic acid: 7.3%

EXAMPLES l2-45 Catalyst were prepared in the similar way to that of Example 1 1, except that the starting materials were adjusted so as to maintain the atomic ratios given in Table 4. As iron, nickel and magnesium components, nitrates; as a tin component, oxide and as a tungsten component, ammonium tungstate were used, respectively. The catalysts were used in the oxidation of methacrolein under substantially the same conditions as those employed in Example 11. The results obtained were given in Table 4.

EXAMPLES 4656 ing the following atomic ratio of elements was obtained.

Said solid was sieved to collect a catalyst within the range of 35 to 100 mesh size. The aforementioned U- shaped reactor was filled with 4 ml of the obtained cat- Table 5 Acrylic Acetic Acrolein acid acid Ex. conversion selectivity selectivity Nos Catalysts 46 M6,,P,Nb,B1,o.,,, 91.3 82.4 3.4 47 M6, P,Nb,13i,o. 85.1 78.7 4.2 48 M6,,P,1 1b .01... 78.2 83.5 3.1 49 M6,,P,Nb,Bi,o., 52.6 81.6 2.7 50 Mo, P,Nb Bi O 89.4 76.3 3.8 51 Mo, P,Nb ,,Bi ,O 81.9 80.1 2.9 52 Mo,,P,Nb,Fe O 91.5 82.3 4.5 53 M6,,1 ,1-1b,1-11,o, 87.4 85.7 3.2 54 M6,,1 ,1-11 ,M ,o., 93.2 80.1 5.6 55 M6,,P,Nb,sn,o,, 85.2 75.4 7.8 56 M6,,P,Nb,w,o,, 86.3 73.5 5.9

EXAMPLE 57 alyst. The reactor was put into the molten salt bath 23.1 grams of 85% orthophosphoric acid dissolved in 50 ml of water were added, under stirring, to the liquid in which were dissolved by heating 423.9 grams of ammonium paramolybdate in 500 m1 of water. 100 ml of heated at 330C. A reactant gaseous mixture composed of 5% of methacrolein, 9% of oxygen, 32% of steam and 54% of nitrogen, the percentages being by volume, was passed through the reactor with a contact time of 2 seconds. The following results were obtained:

The conversion of methacrolein: 81.2%

The selectivity of methacrylic acid: 64.5%

The selectivity of acetic acid: 6.3%

EXAMPLES 58-61 Catalysts were prepared in the similar way to that of Example 57, except that the starting materials were adjusted so as to maintain the atomic ratios given in Table 6. The catalysts were used in the oxidation of methacrolein under substantially the same conditions as those employed in Example 57. The results obtained were given in Table 6:

Table 6 Metha- Methacrylic Acetic crolein acid acid se- Ex. conversion selectivity lectivity Nos. Catalysts 58 Mo PJa o 85.2 49.9 10.3 59 Mo P Ta Q, 52.1 59.6 7.7 60 Mo, l,Ta -,O 80.3 50.7 6.3 61 Mc1, P,,, '1"a,O 82.4 47.4 8.2

REFERENCE EXAMPLES 6 -13 concentration nitric acid were added to the mixture liquid above and then, 44.2 grams of tantalum pentoxide suspended in 200 ml of nitric acid aqueous solution (1:1) were added to the resulting liquid on heating under stirring, followed by adding: 80.8 grams of ferric nitrate dissolved in 100 ml of water therein. Then, the resulting mixture liquid was concentrated by heating under stirring, followed by drying of the resulting slurry at 120C for 24 hours. Thereafter, the dried product was calcined at 400C for 6 hours, whereby a solid having the following atomic ratio of elements was obtained.

Said solid was sieved to collect a catalyst within the range of -100 mesh size. The catalyst was used in the oxidation of methacrolein under substantially the same conditions as those employed in Example 57. The following results were obtained:

The conversion of methacrolein: 90.1%

The selectivity of methacrylic acid: 63.4%

The selectivity of acetic acid: 9.2%

Table 7 EXAMPLES 63-86 M Methacrylic Acetic 30 Catalysts were prepared in thesimtlar way to that of Ref. crolein acid acid se- Example 62, except that the starting materials were adex. conversion selectivity lectivity h i r i S i i b] Catalysts JUSICd SO as to malntaln t e atom c at o g n T e 8. As iron, magnesium and nickel components, nitrates 2 m ng m thereof; as a tin component, oxide thereof and as a X SIZ' E EE' :3 5 5: 35 tungsten, ammonium tungstate were used, respectively. 9 mZ I m M 2- 1. The catalysts were used in the oxidation of methacromg g ig g :3; lein under substantially the same conditions as those 1 I 7111.5 12 M0::P, M ,0 39.4 17.5 9.9 employed in Example 62. The results obtained were 13 Mo, Ni,Mg,O; 15.7 40.3 5.3 given in Table Table 8 Methacrylic Acetic Methacrolein acid acid Examp conversion selectivity selectivity Nos. Catalysts 63 Mo Pfl'a Fmo 85.6 5 3.4 12.2 64 Mo,- P,Ta,Fe O 79.4 5 9.3 9.6 65 M0,,P .T.1,Fe,0,, 59.6 63.7 7.0 66 Mo P Ta Fe O 55.5 39.8 14.5 67 Mo P Ta Fe o 44.1 41.1 9.2 68 Mo P Ta,Fe O 22.2 54.1 7.6 69 Mo P Ta sn O 81.0 57.2 5.2 70 Mo P,Ta,Sn,O., 87.9 53.1 11.8 71 Mo..P.Ta.w,o,., 80.4 60.6 8.7 72 MQ PJa W O 90.5 54.3 13.2 73 Mo P,Ta Fe,, ',O 77.2 52.4 6.5 74 Mo, P., ,,Ta,Fe ,0 82.7 51.3 7.5 75 Mo P Ta Ni O 85.4 7.3 10.1 76 Mo P,Ta,Ni O 89.7 57.3 9.4 77 iu l l gn u 82.1 53.9 6.7 78 Mo P Tu,Mg,O 88.4 58.7 5.4 79 ll I l lL5 4L5 80.3 59.4 5.6 80 M0,,P,T.l,M ,o,, 79.9 61.3 7.8 81 Mo Pflu Nho 83.7 60.0 4.3 82 Mo P,Ta Mg,() 81.5 53.2 8.5 83 Mo ,P Ta,Fc W,O 78.5 53.3 3.2 84 MO P Tfl sn1 -m 85 Mn P,Ta Mg Ni,O 69.3 65.4 7.4 86 Mo P Ta Mgfin o 72.7 56.5 8.]

EXAMPLE 62 65 EXAMPLES 87-92 23.1 grams of 85% orthophosphoric acid dissolved in 50 ml of water were added, under stirring, to the liquid in which were dissolved by heating 423 grams of ammonium paramolybdate in 500 m1 of water. ml of Catalysts obtained in Examples 57, 62, 70, 72, 76 and 78, respectively, were used. The catalysts were used in the oxidation of acrolein under substantially the same conditions as those employed in Example 1, except that the reaction temperature was 365C. The results obtained were given in Table 9:

23.1 grams of 85% orthophosphoric acid dissolved in 50 ml of water were added, under stirring, to the liquid in which were dissolved 423 grams .of ammonium paramolybdate in 700 ml of water. 379 grams of titanium tetrachloride, Ticl dissolved in 200 ml of hydrochloric acid (1:1) were added all at once to the resulting liquid under stirring. Then, the resulting mixture liquid was evaporated by heating under stirring, followed by drying of the resulting cake at 120C for 16 hours. Thereafter, the dried product was calcined at 400C for 12 hours, whereby a solid having the atomic ratio of elements was obtained.

Said solid was sieved to collect a catalyst within the range of 35-l00 mesh size. The aforementioned U- shaped reactor was filled with 4 ml of the obtained catalyst. The reactor was put in the molten salt bath heated at 330C. A reactant gaseous mixture composed of 5% of methacrolein, 9% of oxygen, 32% of steam and 54% of nitrogen, the percentages being by volume, was passed through the reactor with a contact time of 2 seconds. The following results were obtained:

The conversion of methacrolein: 72.3%

The selectivity of methacrylic acid: 53.7%

The selectivity of acetic acid: 8.4%

REFERENCE EXAMPLES 14- 15 Catalysts were prepared in the similar way to that of Example 93, except that the starting materials were adjusted so as to maintain the atomic ratios given in Table 10. The catalysts were used in the oxidation of methacrolein under substantially the same conditions as those employed in Example 93. The results obtained were given in Table 10:

23.1 grams of 85% of orthophosphoric acid dissolved in 50 ml of water were added, under stirring, to the liquid in which were dissolved 423 grams of ammonium paramolybdate in 700 ml of water. 37.9 grams of titanium tetrachloride dissolved in 200 ml of hydrochloric acid (1:1 were added all at once to the resulting liquid under stirring, followed by adding 44.2 grams of tantalum pentoxide, Ta O suspended in 200 ml of nitric acid (1:1) therein. Then, the resulting mixture liquid was evaporated by heating under stirring, followed by drying of the resulting cake at 120C for 16 hours. Thereafter, the dried product was calcined at 400C for 12 hours, whereby a solid having the atomic ratio of elements was obtained.

Said solid was sieved to collect a catalyst within the range of 35-100 mesh size. The aforementioned U- sha'ped reactor was filled with 4 ml of the obtained catalyst. The oxidation of methacrolein was conducted under substantially the same conditions as those employed in Example 93. The following results were obtained:

The conversion of methacrolein: 86.3%

The selectivity of methacrylic acid: 67.5%

The selectivity of acetic acid: 8.1%

EXAMPLES -96 Table 11 Metha- Methacry- Acetic crolein lic acid acid se- Ex. conversion selectivlectivity Nos. Catalysts ity 95 Mo, P,Ti,Nb,O,, 96.2 55.9 12.1 96 Mo P ThSn O, 86.4 53.7 13.5

REFERENCE EXAMPLES l 6- 17 Catalysts were prepared in the similar way to that of Example 94, except that the starting materials were adjusted so as to maintain the atomic ratios given in Table 12. The catalysts were used in the oxidation of methacrolein under the same conditions as those employed in Example 94. The results obtained were given in Table 12:

Table 12 Metha- Methacrylic Acetic Rcf. crolein acid acid seex. conversion selectivity lectivity Nos. Catalysts l6 Mo Ti Ta oaus 23.8 18.5 9.3 17 Mo Ti NmO 31.4 21.7 8.6

EXAMPLES 97-100 Catalysts obtained in Examples 9396 were used, respectively, for the oxidation of acrolein under substan tially the same conditions as those employed in Exam- Example 94, except that the starting materials were adjusted so as to maintain the atomic ratios given in Table 15. The catalysts were used for the oxidation of acrolein under substantially the same: conditions as those ple 93, except that the reaction temperature was employed in Example 94. The results obtained were 360C. The results obtained were given in Table 13: given in Table Table I5 Acrylic Acrolein .acld Acetic acid Ex. conversion selectivity selectivity Nos. Catalysts 105 Mo,,P,Ti,Ta,o,, 84.7 69.2 11.1 106 Mo,,1 ,Ti,Ta ,o,,, 78.3 75.8 8.5 107 Mo,,P ,Ti,Ta,o,, 58.5 74.0 (1.9 108 Mo,,P,Ti,,Ta,O,,,, 54.4 38.7 13.4 109 Mo,,P,Ti,Ta,,o,, 43.0 40.2 10.3 110 M0,,P ,T1,Ta,0, 23.3 55.0 8.7 1 1 1 Mo P Ti Ta O 78.3 69.4 7.7 112 Mo,,P,, ,Ti,Ta,o,, 83.8 72.2 8.0

Table 13 EXAMPLES ll3-l l9 imf' Catalysts were prepared in the similar way to thatof Ex. version lcctivity lLLllVily Example 93, except that the starting materials were ad- 1 s I I l a o usted so as to maintain the atomic ratios given in Table 97 Mulzpl-nlom 33,2 65,7 4L3 16. The catalysts were used for the oxidation of meth- 98 mz t t u a t acrolein under substantially the same conditions as 3: :2 7 those employed In Example 93. .lhe results obtained H were given in 'lahle l6:

'lable l6 Acrylic Methacrolein acid Acetic acid Example conversion selectivity selectivity Nos. Catalysts (7(7) (70) l l3 Mo Pfl'i Ta o 89.8 44.4 l0.3 1 l4 Mo, P,Ti,Ta O 78.1 53.7 8.2 115 Mo nmn o 28.3 76.8 6.0 1 l6 Mo P Ti Ta O 76.6 63.9 8.6 ll7 Mo P Ti,-,Sn O 93,5 42,] 9 7 ll8 Mo P,Ti,Sn O., 92.0 43.6 11.8 [19 Mo, P Ti,Sn,O 31.2 64.5 7.5

EXAMPLES 101 -104 Catalysts were prepared in the similar way to that of Example 93, except that the starting materials were adjusted so as to maintain the atomic ratios given in Table 14. The catalysts were used in the oxidation of methacrolein under the same conditions as those employed in Example 93. The results obtained were given in Table 14:

Table 14 Metha- Methacry- Acetic crolein lic acid acid se- Ex. conversion selectivlectivity Nos. Catalysts (70) ity (71) 71) 101 Mo, P,Ti;,O.,,, 81.3 47.6 1 1.2 I02 Mo P ThO 45.0 69.2 8.4 12 l (L-' 39.b 7L6 55.7 7.3 104 Mo P ThQ- 80.8 49.0 9.3

EXAMPLES l05-l l2 Catalysts were prepared in the similar way to that of What we claimed is:

1 A process for preparing acrylic acid or methacrylic acid which comprises reacting acrolein or methacrolein with molecular oxygen in vapor phase at a temperature of from 250 to 450C, in the presence of a catalyst consisting essentially of (a) molybdenum, (b) phosphorus, (c) at least one element selected from the group consisting of niobium, tantalum and titanium, and (d) oxygen.

2. A process as set forth in claim I, wherein said catalysts having the empirical formula:

wherein X is at least one element selected from the group consisting of niobium, tantalum and titanium, a is a number of 0.1 to 5, B is a number of 0.1 to 10, y is a number of 36 to 81.

3. A process for preparing acrylic acid or methacrylic acid which comprises reacting acrolein or methacrolein with molecular oxygen in vapor phase at a temperature of from about 250 to about 450C, in the presence of a catalyst consisting essentially of (a) molybdenum (b) phosphorus, (c) at least one element selected from the group consisting of niobium, tantalum and titanium, (d) oxygen and (e) a member selected from the group consisting of tin, magnesium, tungsten, tin and magne 15 sium, tin and tungsten, iron and tungsten, and magnesium and nickel.

4. A process as set forth in claim 3, wherein said catalysts having the empirical formula:

wherein X is at least one element selected from the group consisting of niobium, tantalum and titanium; Y is a member selected from the group consisting of tin, magnesium, tungsten, tin and magnesium, tin and tungsten, iron and tungsten, and magnesium and nickel; a is a number of 0.l to B is a number of 0.1 to 8 is a number of0.l to 10 and e is a number of 38 to l l l.

S. A process as set forth in claim 1, wherein said cataphomolybdate is used. 

1. A PROCESS FOR PREPARING ACRYLIC ACID OR METHYLACRYLIC ACID WHICH COMPRISES REACTING ACROLEIN OR METHYLACROLEIN WITH MOLECULAR OXYGEN IN VAPOR PHASE AT A TEMPERATUE OF FROM 250* TO 450*C, IN THE PRESENCE OF A CATALYST CONSISTING ESSENTIALLY OF (A) MOLYBDENUM, (B) PHOSPHORUS, (C) AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF NIOBIUM, TATALUM AND TITANIUM, AND (D) OXYGEN.
 2. A process as set forth in claim 1, wherein said catalysts having the empirical formula: Mo12-P -X -O wherein X is at least one element selected from the group consisting of niobium, tantalum and titanium, Alpha is a number of 0.1 to 5, Beta is a number of 0.1 to 10, gamma is a number of 36 to
 81. 3. A PROCESS FOR PREPARING ACRYLIC ACID OR METHACRYLIC ACID WHICH COMPRISES REACTING ACROLEIN OR METHACROLEIN WITH MOLECULAR OXYGEN IN VAPOR PHASE AT A TEMPERATURE OF FROM ABOUT 250* TO ABOUT 450*C, IN THE PRESENCE OF A CATALYST CONSISTING ESSENTIALLY OF (A) MOLYBDENUM (B) PHOSPHORUS, (C), AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF NIOBIUM, TANTALUM AND TITANIUM, (D) OXYGEN AND (E) A MEMBER SELECTED FROM THE GROUP CONSISTING OF TIN, MAGNESIUM, TUNGSTEN, TIN AND MAGNESIUM, TIN AND TUNGSTEN, IRON AND TUNGSTEN, AND MAGNESIUM AND NICKEL.
 4. A process as set forth in claim 3, wherein said catalysts having the empirical formula: Mo12-P -X -Y -O wherein X is at least one element selected from the group consisting of niobium, tantalum and titanium; Y is a member selected from the group consisting of tin, magnesium, tungsten, tin and magnesium, tin and tungsten, iron and tungsten, and magnesium and nickel; Alpha is a number of 0.1 to 5; Beta is a number of 0.1 to 10; delta is a number of 0.1 to 10 and epsilon is a number of 38 to
 111. 5. A process as set forth in claim 1, wherein said catalysts are prepared by concentrating a solution or suspension containing requested components, drying the resulting concentrate, calcining the dried product at a temperature of from 250* to 450*C, for 1 to 48 hours in air, and grinding into the desired size.
 6. A process as set forth in claim 5, wherein as the source of molybdenum component, being one of said requested components, ammonium paramolybdates are used.
 7. A process as set forth in claim 5, wherein as a common source for molybdenium and phosphorus components, being two of said requested components, phosphomolybdate is used. 